They will also launch from B52's.
Yes,
But their normal flight profile takes then down close to the surface (couple of hundred feet) so the terrain following radar (imagine how much success it had following the ocean) can image the terrain below. And for you sharpshooters out there, it uses inertal guidance till it gets over land, then establishes where it is relative to it's terrain database, then make corrections to close on it's target.